1. Field of the Invention
The present invention relates to a display advance system for a word processor having a video screen, and particularly to such a system wherein actuation of a DISPLAY ADVANCE control key causes the next consecutive section of a stored page of text to be displayed on the screen.
2. Description of the Prior Art
Use of a word processing system offers considerable benefits over conventional typing of correspondence or text material. Errors readily can be corrected, and all forms of text editing can be accomplished, including the insertion, deletion and rearrangement of words, lines or paragraphs of text. Rapid letter-perfect printout is achieved.
Word processors having video screen displays are particularly useful. As the operator keys in new material, the text immediately is displayed on the screen. Errors can be spotted and corrected prior to printout. Words can be moved automatically to compensate for insertion or deletion of material. Rearranged text can be viewed in its new position, and the entire page can be verified visually prior to printout. Thus such a videoscreen-based text-processing system offers significant advantages over "blind" automated word-processing systems wherein the corrections, insertions or deletions are made in memory, but can not be seen by the operator until a hard copy printout is produced.
In the past, the widespread acceptance of video display word processors has been impeded by the high cost of such systems. Part of this high cost was attributed to the speed requirements of the electronic circuitry required to generate a video display of a full page of text. For example, a video screen capable of displaying 68 lines of text, each 102 characters long, has available an average of 2.4 microseconds to generate each character on the screen, at a frame rate of 60 frames per second. The high speed electronic circuitry required to facilitate such a display significantly increases the equipment cost.
A substantial decrease in system cost is achieved by providing a word processor with a video screen which displays only a portion, typically one-third, of a full page of text. Such an arrangement gives the operator all of the benefits of video display text processing, but reduces the electronics speed requirements by a factor of almost three. Thus for a 25 line display having a frame rate of 60 frames per second, with 102 characters per line, and average time of 6.5 microseconds is available for generating each character.
An apparent problem associated with a word processor in which only one-third of a page is displayed relates to proofreading. As the operator reads down toward the bottom of the displayed text section, it becomes necessary to advance the display to show the following sections of text. In the past, this has required the tedious scrolling or "rolling up" of the display one line at a time. Such scrolling is distracting to the proofreading operation.
A principle object of the present invention is to provide a display advance system for a videoscreen word processor in which, when a DISPLAY ADVANCE control key is depressed, the display automatically advances to the next section of text. Thus if the video screen normally displays one-third of a full page of text, depression of the DISPLAY ADVANCE control key will cause the next one-third section immediately to appear. In a preferred embodiment, if the bottom one-third section of the text currently is being displayed, the display advance operation next will cause the top one-third of the same page to appear. Advantageously, each section of display begins with a repeat of the bottom line of the previous section, thereby aiding smooth comprehension of the text being proofread.
Certain display advance techniques have been disclosed in the past. For example, the U.S. Pat. No. 3,706,075 to Fredrickson et al describes the proofreading problem in conjunction with a text editing system for newspaper copy. The Fredrickson system employs a cathode ray screen which may be "rolled up" or "rolled down" one line at a line as the editing proceeds. This is facilitated by using a recirculating shift register-type memory having a character position capacity substantially greater than can be displayed at one time on the screen. Operation of a "roll-up" or "roll-down" key toggles by one count the contents of a register which controls line accessing of the data in the recirculating memory.
Another one-line-at-a-time scrolling system is disclosed in the U.S. Pat. No. 3,956,739 to Ophir et al. In that system, which is not specifically intended for word processing, the frame address memory is incremented by a value corresponding the number of characters in each displayed row. This incrementing typically occurs once each second, so that the display appears to roll upward continuously.
Another system for enabling data to appear to be travelling up or down across the face of the display tube is disclosed in the U.S. Pat. No. 3,593,310 to Kievit. Here, the scrolling is accomplished by altering the memory storage position of the data to be displayed. For a one line shift, the entire set of data to be displayed is read out of the memory from one location and reentered into the memory at a shifted location from which the new display is generated.
A different implementation of "roll-up" is disclosed in the U.S. Pat. No. 4,020,483 to Baumgartner. Here, the CRT deflection signals are modified to cause row-by-row displacement of the characters in the upward direction. The U.S. Pat. No. 3,540,012 to Ehrman shows a system for line insertion or deletion in a CRT display.
The U.S. Pat. No. 3,618,032 to Goldsberry et al discloses another method by which circuit speed can be reduced in a videoscreen word processor. In this system, only a few lines, typically five, of information are displayed in a portion of a relatively large CRT screen. Deflection control circuitry is used to locate the lines on the CRT in a position corresponding to the location of those lines in the stored page of text. For example, if the five lines are in the middle of the text, they will be displayed at the center of the CRT tube.